1. Field of the Invention
The present invention relates to a switch witho contacts which includes an electromagnetic relay having a movable contact member made of a leaf spring for switching on and off a DC current and the like.
2. Description of Prior Art
In general, in the case of switching on and off a DC current by using a relatively small electromagnetic relay in which a movable contact member is made of a leaf spring, the resistance load of about 1A at the DC voltage of 100 V is the breaking limit value. In the case of a voltage or current larger than those values, the breaking cannot be performed due to an arc when the contacts are switched off.
Therefore, hitherto, for instance, as shown in FIG. 9, an electromagnet block 104 is constructed by winding a coil 103 around an iron core 102 fixed to a yoke 101. A base end portion of a movable contact member 106 made of a leaf spring is fixed to one end portion of a movable iron member 105 which is pivotally supported to the yoke 101 at an almost central position thereof (the pivotal supporting structure is not shown in the diagram). A movable contact 111 which is come into contact with and is away from fixed contact 109 or 110 of a pair of fixed contact members 107 and 108 is attached to a tip portion of the movable contact member 106. Permanent magnets 112 and 113 are arranged at positions such as to sandwich the movable contact 111 with an interval. That is, an electromagnetic force is generated on the basis of the Fleming's left-hand rule by an arc current I (FIG. 9) which is generated when the movable contact 111 is away from (switched off) the fixed contact 109 or 110 and by a magnetic flux .phi. of the permanent magnets 112 and 113 in the direction perpendicular to the direction of the arc current I. An arc Q which is generated when the contact is switched off is pushed to the outside and is extinguished as shown in FIGS. 10a to 10c by such an electromagnetic force.
However, according to the above construction, one end of the arc column always exists at the movable contact 111 or movable contact member 106 as shown in FIGS. 10a to 10c for the period of time from the generation of the arc Q (at the time of the switch-off of the contact) to the extinguishment of the arc. Therefore, the movable contact 111 and movable contact member 106 are heated by the arc heat, causing the abrasion of the contacts and the deterioration of the spring characteristic of the movable contact member 106. Particularly, in the case of a large current or inductive load, since it takes a long time until the arc is extinguished, the temperature of the movable contact member 106 becomes high and the spring characteristic remarkably deteriorates, so that the switching operation is obstructed.